ARMY TM 9-6115-604-12
NAVY NAVFAC P-8-633-12
(2)
Reverse Power Relay K109 Reverse power relay K109 is located in the upper section of cabinet B and protects
generator G1 against motoring on loss of drive power from the engine (the engine shuts down). The relay
compares the phase angle relationship of voltage and current that determines direction of power in the generator.
When power is sensed flowing into the generator set at 13 to 26 amperes (or more), relay K109 will pick up within
12 cycles to energize self-latching relay A11K1 in the annunciator alarm system. Annunciator horn LS1 sounds
and REVERSE POWER fault light A9DS10 on the annunciator panel flashes. A11K1 also energizes circuit breaker
trip relay K30. Relay K30 energizes the trip coil in load circuit breaker CB101, opening the breaker to disconnect
generator G1 from the bus. The engine will continue to run but load circuit breaker CB 101 cannot be closed until
the annunciator alarm system has been manually reset via ANNUNCIATOR RESET pushbutton S12 on the upper
door of cabinet A.
(3)
Overvoltage Relay K110. Overvoltage relay K110 is located inside the upper part of cabinet B and monitors the
voltages at the secondaries of generator instrument transformers T104, T106, and T107. The generator
instrument transformers are high accuracy (0.6 percent) 20:1 step-down transformers. Each transformer is tied to
an output line of generator G1 (T104 to phase T1, T107 to phase T2, and T106 to phase T3). Overvoltage relay
K110 monitors the three phases and tops whenever the highest voltage input exceeds 239 ~ 5 V ac for more than 3
1 seconds (higher overvoltages will result in shorter tripping times). TIME DELAY ADJUST, on the face of the
relay, is normally set to "A". Higher settings (“B”, "C”, or "D") result in greater delay before the relay trips
(normally 5, 7, and 9 seconds, respectively). 239 V ac at the secondary of transformer T104, T106, or T107
represents a generator G1 line voltage of 4780 V ac, equivalent to 115 percent overvoltage at 60 hertz, or a 126
percent overvoltage at 50 hertz. When tripped, relay K110 energizes a slave relay, K9. Relay K9 energizes
self-latching relay A10K7 in the annunciator alarm system. Annunciator horn LS1 sounds and OVERVOLTAGE
fault light A9DS7 on the annunciator panel flashes. A10K7 also energizes fault shutdown relays K20A and K20B
Relay K20A deenergizes self-latching engine run relay K15B. As a result engine fuel solenoid L1 loses power,
closes, and cuts off fuel to the engine; the engine shuts down. Relay K20B energizes circuit breaker tap relay
K30. Relay K30 energizes the trip coil in load circuit breaker CB101, opening the breaker to disconnect generator
G1 from the bus. The generator set cannot be restarted until the annunciator alarm system is reset via
ANNUNCIATOR RESET pushbutton S12 on the upper door of cabinet A.
(4)
Undervoltage Relay K111. Undervoltage relay K111 is located inside the upper part of cabinet B, is normally
energized, and, like overvoltage relay K110, monitors the voltages at the secondaries of generator instrument
transformers T104, T106, and T107. These transformers are described in step (3), above. Undervoltage relay
K111 will deenergize whenever the lowest input voltage to the relay falls below 177 V ac for more than 1.5
1
seconds (lower undervoltages will result in shorter tripping times). TIME DELAY ADJUST, on the face of the
relay, is normally set to “A". Higher settings ("B", "C", "D", or `”E") result in greater delay before the relay trips
(nominally 2 5, 4, 6, and 10 seconds, respectively). 177 V ac at the secondary of transformer T104, T106, or
T107 represents a generator G1 line voltage of 3540 V ac, equivalent to 15 percent undervoltage at 60 hertz, or 7
percent undervoltage at 50 hertz. During generator startup, fault bypass relay K17A prevents relay K111 from
causing a generator set undervoltage indication until approximately 10 seconds after engine speed has climbed
above 600 rpm. 10 seconds after the engine reaches 600 rpm, generator G1 line voltage will exceed 3540 V ac,
causing the undervoltage relay K111 to energize and close its contacts. Ten seconds after reaching 600 rpm,
relay K17A energizes, thus arming the undervoltage fault shutdown circuits. If generator G1 line voltage
subsequently falls below 3540 V ac, relay K111 will deenergized, and open its contacts so that annunciator alarm
system self-latching relay A10K8 is energized. Annunciator horn LS1 will sound and UNDERVOLTAGE fight
A9DS8 on the annunciator panel will flash. Relay A10K8 also energizes circuit breaker trip relay K30. Relay K30
energizes the trip coil In load circuit breaker CB101, opening the breaker to disconnect generator G1 from the bus
The engine will continue to run, but load circuit breaker CB101 cannot be closed until the annunciator alarm
system has been reset via ANNUNCIATOR RESET pushbutton S12 on the upper door of cabinet A.
(5)
Overcurrent Relay K114. Solid state overcurrent relay K114 is panel mounted on upper cabinet A door and
monitors the current through instrument current transformers CT10, CT11, and CT12. Instrument current
transformers CT10, CT11, and CT12 sense the current through generator G1 output lines T3, T2, and T1,
respectively. At rated load, each output line carries 130 amperes, Inducing a current of 3.71 amperes in each
current transformer. To properly monitor each phase, the current pickup taps on the front panel of relay K114
must be set to "4" for each phase, “4” being the approximate output, in amperes, of each instrument current
transformer CT10 through CT12. The TIME dial on the front panel of K114 is set to "10" with its associated
vernier, marked ADJ, set fully counterclockwise These settings establish the time delay curve that K114 trips on.
a continuous 130 percent overload (line current 169 amperes, current transformer current 4 83 amperes) will
cause overcurrent relay K114 to trip after 15 to 25 seconds. Tripping is accomplished by the gating of an SCR
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